PCM1754: VOUT-L、VOUT-R have noise, but cut off PIN1, PIN2, VOUT-L、VOUT-R noise are disappear.

WU YISYUAN

Expert 2165 points

Part Number: PCM1754

Hi,

I used PCM1754 have a problem.

We have found that recording then playing, the voice have noise.

And we measure PIN VOUT-L、VOUT-R, find the noise signal. the waveform as below.

when I del PIN1 and PIN2, the output noise is disappear, the waveform as below:

output voice have no noise.

schematic

What is the reason, what is the solution?

Thanks.

over 7 years ago

0 Paul_Frost over 7 years ago

TI__Guru 55043 points

Hi Wu,

That is a strange output! Can you please share some information about your configuration, such as a schematic? In addition, please verify that you are sending the correct I2S format and the device supplies are stable and correct.

Thanks!
Paul

0 WU YISYUAN over 7 years ago in reply to Paul_Frost

Expert 2165 points

Hi Paul,
Update the schematic.
this issue is find an analog noise signal, even cut off the I2C to PIN2(DATA) the noise still exist.
But cut off (DA_BCLK) connect to PIN1(BCK) that the analog noise signal is disappear.

0 Paul_Frost over 7 years ago in reply to WU YISYUAN

TI__Guru 55043 points

Hi Wu,

What is the output after the low-pass filter look like? The output of pin 7 and 8 will look noise as there is a lot of oversampling going on in the output. Disabling the I2S inputs will basically turn off the DAC so it is hard to say that they are cause of the noise.

Thanks!

0 Paul_Frost over 7 years ago in reply to Paul_Frost

TI__Guru 55043 points

Hi Wu,

Any updates?

0 WU YISYUAN over 7 years ago in reply to Paul_Frost

Expert 2165 points

hi Paul,

The front end of the DAC is connected to an echo cancellation module (as a host).

The DAC input is I2S's digital voice signal with a sampling rate of 16KHz.

The frequency of the external oscillator of DAC is 12.288MHz,

PIN 7, PIN8 back end of the DAC is connected to the Audio Codec microphone input interface.

0 Paul_Frost over 7 years ago in reply to WU YISYUAN

TI__Guru 55043 points

Hi Wu,

How does the output look on both the left and right side of C313?

0 Matthew Sauceda over 7 years ago in reply to Paul_Frost

TI__Genius 11750 points

Hi Wu,

Just to add to the questions posed by my colleague. Can you provide another oscilloscope capture of the noise, but triggered so we can analyze the periodicity of the signal. If the noise has the same frequency components as BCLK, then there is the possibility of the noise coupling into the analog section of the PCB. Another thing to note is if the oscilloscope probes are measuring both analog and digital signals. I've seen instances where crosstalk/coupling occurs between these signals through the oscillosope itself, therefore another recommendation is to only use probes for analog, or digital measurements, but not for both at the same time.

Best Regards,
Matt

0 Paul_Frost over 7 years ago in reply to Matthew Sauceda

TI__Guru 55043 points

Hi Wu,

Any updates?

Paul

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PCM1754: VOUT-L、VOUT-R have noise, but cut off PIN1, PIN2, VOUT-L、VOUT-R noise are disappear.